That depends alot on your location and what codes your
jurisdiction has adopted. From the 2006 International Plumbing
Code, "water service pipe and the building sewer SHALL be separated
by 5 feet of undisturbed or compacted earth." There are exceptions,
1. "the required separation distance shall not apply where the
bottom of the water service pipe within 5 feet of the sewer is a
minimum of 12 inches above the top of the highest point of the
sewer and the pipe materials conform to Table 702.3. 2. water
service pipe is permitted to be located in the same trench with a
building sewer, provided such a sewer is constructed of materials
listed in Table 702.3. 3. the required separation distance shall
not apply where a water service pipe crosses a sewer pipe, provided
the water service pipe is sleeved to at least 5 feet horizontally
from the sewer pipe center-line on both sides of such crossing with
pipe materials listed in Table 605.3, 702.2, or 702.3." So, no,
there is no minimum separation IF the materials you are using bear
the correct ASTM #. (Your building sewer pipe will probably have
ASTM F 891 stamped on it.)
